Numerical analysis of inter-panel pillars in the bump prone conditionals of the Alardinskaya mine

The purpose of the paper is to substantiate the width of the barrier and yield pillars for the application of a new seam development scheme in the conditions of the Alardinskaya mine (Russia). The Alardinskaya mine develops gas-bearing coal seams that are prone to spontaneous combustion and are hazardous due to rock bumps, which leads to frequent accidents. The analysis of the world experience of mining seams being hazardous to rock bumps showed that safe mining with longwalls can be provided by a system of inter-panel pillars: very wide barrier pillar and two yield pillars. Numerical modeling using the finite element method was carried out to assess the possibility of reducing the barrier pillar width in order to decrease the volume of coal losses in the subsoil. The model of rock massif was created in Ansys mechanical software. Numerical modeling of the longwall panel development with longwalls was carried out at various widths of broad and yield pillars. The analysis outcomes of the vertical stresses diagrams in the seams are presented for different parts of the longwall panel. The rational parameters of the pillar system, ensuring the minimization of the reference pressure influence from the previously worked-out column and the reference pressure of the operating longwall, are determined as a result of numerical analysis. The conclusion is made about the expediency of the technological scheme application proposed by the authors in the conditions of the Alardinskaya mine to reduce the endogenous fire hazard and the danger of rock bumps.

Mining-induced deformation in potash yield pillars, Vanscoy, Saskatchewan

Mining-induced deformation of potash yield pillars in the Cominco potash mine at Vanscoy, Saskatchewan, has been documented by mapping deformational structures, determining changes in pillar width and in thicknesses of potash and interbedded clay layers, and analyses of rock fabrics in samples collected from three yield pillars. Pillar deformation over a period of 8 years can be shown to have involved progressive bulk rock flattening, followed by development of shear zones at pillar corners, development of shear wedges at pillar margins, and detachment of these wedges into adjacent rooms. Furthermore, this sequence appears to be repetitive. Strain in halite involves fracturing and displacement and rotation of fragments, strain in sylvite is continuous, and grain boundary sliding has been an important mechanism in the deformation. Although the fabric anisotropy cannot be used to assess total bulk rock strain, the component of strain related to sylvite shape change has been examined during progressive failure of the pillars. The values of strain in the principal strain directions based on sylvite shape are estimated as 42% shortening in the subvertical direction, 37% subhorizontal elongation perpendicular to the original openings, and 25% subhorizontal elongation parallel to the original openings. Key words : yield pillar, potash, fabric analysis, induced deformation.